public Dictionary<string,List<long>> ToOIDDictionary()

var kg_layer = MapView.Active.Map.GetLayersAsFlattenedList()
                .OfType<KnowledgeGraphLayer>().FirstOrDefault();
if (kg_layer == null)
  return;

QueuedTask.Run(() =>
{
  //Get the existing kg layer id set and convert to a dictionary
  var layer_id_set = kg_layer.GetIDSet();
  var dict = layer_id_set.ToOIDDictionary();//Empty list means all records

  //Create an id set from a dictionary
  var dict2 = new Dictionary<string, List<long>>();
  dict2.Add("Enity_Or_Relate_Type_Name1", null);//Null means all records
  dict2.Add("Enity_Or_Relate_Type_Name2", new List<long>());//Empty list means all records
  dict2.Add("Enity_Or_Relate_Type_Name3", 
    new List<long>() {  3,5,9, 101, 34});//Explicit list of ids
  //dict2.Add("Enity_Or_Relate_Type_Name4",
  // new List<long>() { etc, etc });

  //Create the id set
  var idset = KnowledgeGraphLayerIDSet.FromDictionary(kg, dict2);

  //Can be used to create a layer, link chart, append to link chart, etc...
});

QueuedTask.Run(() =>
{
  var idSet = kgLayer.GetIDSet();

  // is the set empty?
  var isEmpty = idSet.IsEmpty;
  // get the count of named object types
  var countNamedObjects = idSet.NamedObjectTypeCount;
  // does it contain the entity "Species";
  var contains = idSet.Contains("Species");

  // get the idSet as a dictionary of namedObjectType and oids
  var oidDict = idSet.ToOIDDictionary();
  var speciesOIDs = oidDict["Species"];

  // alternatively get the idSet as a dictionary of 
  // namedObjectTypes and uuids
  var uuidDict = idSet.ToUIDDictionary();
  var speciesUuids = uuidDict["Species"];

});